1. Field of the Invention
The present invention relates to a lenticular lens array and an image display device including the same, and more particularly, to a lenticular lens array type dimension-switchable image display device that is able to switch from a two dimensional mode into a three dimensional mode or from the three dimensional mode into the two dimensional mode.
2. Discussion of the Related Art
A technology of producing three dimensional (3-D) images including 3-D stereoscopic images from two dimensional (2-D) images can be used in display technologies, aerospace technologies, etc. The technology using ripple effects to produce 3-D images can not only be used in applications for high definition televisions (HDTV), but also can be used in a variety of other applications.
The technology of producing 3-D stereoscopic images includes a volumetric type, a holographic type, and stereoscopic type. The volumetric type uses psychological illusions to create illusory perception along a depth direction. When observers receive 3-D computer graphical images on a large screen having a wide view angle, the observers can experience viewing an optical illusion. By calculating and implementing various factors in 3-D computer graphics technology, images can be displayed to give the observers a 3-D effect on movement, brightness, shade, etc. An example of this kind of volumetric type of display is an IMAX™ movie. In an IMAX™ movie, two camera lenses are used to represent images for the left and right eyes. The two lenses are separated by an average distance between a human's eyes. By recording images on two separate rolls of film for the left and right eyes, and then projecting them simultaneously, the viewers can be tricked into seeing a 3D image on a 2D screen. The holographic type is known to be the most remarkable technology for displaying 3-D stereoscopic images. The holographic type can be further divided depending on the light source that is used. For example, there are holographic displays using laser and holographic displays using white light. The stereoscopic type uses psychological effects to create 3-D images. In normal vision, human eyes perceive views of the world from two different perspectives due to the spatial separation of two eyes. The spatial separation between typical eyes is about 65 mm. In order to assess the distance between objects, the brain integrates the two images obtained from each eye. By integrating two images, we are able to perceive 3-D images. The above method of perceiving a 3-D image is referred to as a stereography phenomenon. The stereoscopic type can be divided into a glasses type and a glasses-free type depending on whether glasses are adopted. The glasses-free type uses a parallax barrier, a lenticular lens array, or an integral lens array, etc. Among these, the lenticular lens array is widely under research today since observers can see 3-D images simply by disposing a lenticular lens on a display panel without any other equipment.
FIG. 1 is a schematic cross-sectional view of a lenticular lens array type image display device according to the related art. As shown in FIG. 1, the lenticular lens array type image display device 10 includes a display panel 20 and a lenticular lens array 30. The display panel 20 displays the 2-D images for both left and right eyes. The lenticular lens array 30 assigns different viewing zones for the 2-D images according to the left and right eyes, respectively.
The display panel 20 is a flat panel display (FPD) device, examples of which include a cathode ray tube (CRT), a liquid crystal display (LCD) device, an organic light emitting display (OLED) device, a plasma display panel (PDP), and a field emission display (FED) device. First and second pixels PL and PR are alternately arranged on the display panel 20. The first pixel PL displays images for the left eye, and the second pixels PR displays images for the right eye. The lenticular lens array 30 includes a lenticular lens 32. The lenticular lens 32 has a half-cylinder shape and is regularly arranged.
The 2-D images emitted from the display panel 20 pass through the lenticular lens array 30 to reach the left and right eyes of an observer 40. The brain integrates the 2-D images obtained from each eye to perceive a 3-D image.
The lenticular lens array may include a liquid crystal layer. In this case, whether the liquid crystal layer functions as the lenticular lens is determined by the voltage that is supplied to the liquid crystal layer. When the liquid crystal layer functions as the lenticular lens, the image display device produces the 3-D images. When the liquid crystal layer does not function as the lenticular lens, the image display device produces the 2-D images. The switching between the two functions can be obtained because liquid crystal molecules in the liquid crystal layer have an ordinary refractive index and an extra-ordinary refractive index due to their an optical anisotropy and polarization properties. These optical properties can be changed when a voltage is applied to the liquid crystal molecules. In other words, it is possible to convert the 3-D display mode into a 2-D display mode by changing the applied voltage.
The lenticular lens array type image display device using the liquid crystal layer as the lenticular lens is further demonstrated in FIGS. 2A and 2B. FIGS. 2A and 2B are cross-sectional views that demonstrate the generation of a 2-D mode and a 3-D mode, respectively according to the related art. As shown in FIGS. 2A and 2B, a lenticular lens array type image display device 110 includes a display panel 120 and a lenticular lens array 130. When the lenticular lens array type image display device 110 is in the 2-D mode, the lenticular lens array 130 does not refract the 2-D images output from the display panel 120. Accordingly, the observer perceives a 2-D image. However, when the lenticular lens array type image display device 110 is in the 3-D mode, the lenticular lens array 130 refract the 2-D image from the display panel 120 such that the observer perceives a 3-D image.
The lenticular lens array 130 includes first and second substrates 132 and 134, first and second transparent electrodes 142 and 152, a transparent replica layer 154, first and second alignment layers 144 and 156, and a liquid crystal layer 160. The first and second substrates 132 and 134 face each other. The first and second transparent electrodes 142 and 152 are formed on inner sides of the first and second substrates 132 and 134, respectively. The transparent replica layer 154 is formed on the second transparent electrode 152. The transparent replica layer 154 has a plurality concave portion such that half-cylinder shaped cell spaces A are defined. The first and second alignment layers 144 and 156 are formed on the first transparent electrode 142 and the transparent replica layer 154, respectively. Accordingly, the second alignment layer 156 has a half-cylinder shape. The liquid crystal layer 160 functions as the lenticular lens and is formed between the first and second alignment layers 144 and 156. In other words, the liquid crystal layer 160 is formed in the cell space A. The replica layer 154 functions as a mold providing the half-cylinder shape, and not as an electrical means.
The liquid crystal layer 160 may include a nematic material. By controlling the electric field between the first and second transparent electrodes 142 and 152, the liquid crystal layer 160 can function either as a transparent layer in the 2-D mode and as a lenticular lens in the 3-D mode. In particular, as shown in FIG. 2A, when zero voltage is supplied between the first transparent electrode 142 and the second transparent electrode 152, the liquid crystal molecules have same orientations as the initial state. Accordingly, the liquid crystal layer 160 does not function as the lenticular lens. In this state, the image display device 110 is in the 2-D mode. However, as shown in FIG. 2B, when a voltage is supplied between the first and second transparent electrodes 142 and 152 to induce the electric field between the first and second transparent electrodes 142 and 152, the liquid crystal molecules rearrange. Accordingly, the liquid crystal molecules are aligned directionally, as shown in the arrows of FIG. 2B. In this state, the lenticular lens array type image display device 110 is in the 3-D mode.
Since the replica layer 154 and the liquid crystal layer 160 should be formed between the first and second transparent electrodes 142 and 152, a distance between the first and second transparent electrodes 142 and 152 is several tens of micrometers larger than that of a conventional LCD device. The density of the electric filed between the first and second transparent electrodes 142 and 152 is directly proportional to a voltage difference between the first and second transparent electrodes 142 and 152 and inversely proportional to a distance between the first and second transparent electrodes 142 and 152. Therefore, the lenticular lens array type image display device 110 requires a higher driving voltage when compared to the conventional LCD device, leading to increased power consumption.